As a 121 captain, I can tell you I can quickly tell who instructed and who didn't. Unfortunately, it is also painfully obvious in our training center who never instructed as a CFI also.

Instructing teaches you CRM and person skills that will help you in the future. It also builds great confidence. I got to a point that I could see a student's mistakes coming a mile away. It was like being a Kung Fu master and watching an unskilled person throw a punch at you--you had plenty of time to step out of the way or correct the problem.